1. Field of the Invention
The present invention relates generally to timing devices. More particularly, the invention concerns a novel fluid operated timing device in which the timing interval is determined by the rate at which the fluid flow through a precisely configured rate control frit upon being forced through the frit by an energy source in the form of a compressible elastomeric member.
2. Discussion of the Prior Art
Numerous types of mechanical, electrical and chemical timing devices have been suggested in the past. These devices have been used in countless systems which require means for establishing a period of time between the occurrence of two events. For example, timing devices are frequently used to switch relay contacts, to open and close fluid control valves, and to control the frequency of delivery of medicaments to a patient.
Perhaps the most commonly used prior art timing devices are electrical and electronic timers. However, such timers are often quite complex, expensive to manufacture and maintain and, of course, require an electrical power supply. An alternative to the electronic timer is the fluid operated timer which typically uses a control fluid such as a liquid or a gas as the timing medium. Often the fluid-operated timer is mechanically coupled with a valve in such a way that, when a preselected period of time elapses, the timer causes the valve to either open or close, thereby regulating flow of fluid.
A common type of fluid operated timer is the so-called dash pot type of delayed actuator. This type of mechanism typically includes a piston disposed within a fluid filled cylinder. As the piston is moved through the cylinder, fluid is forced through a circumferential gap between the piston and the cylinder wall so that the piston gradually changes from a first state to a second state. Another type of frequently used mechanism is the rotary plate delayed actuator. This type of actuator is often used to slow the motion of cassette tape machine doors and record player armatures. Typically these devices employ a pair of parallel plates that are separated by a layer of viscous fluid. Torque is applied to one of the plates while the other is held fixed and the viscous drag of the fluid slows the motion to the movable plate.
Exemplary of prior art mechanical timers are those described in U.S. Pat. No. 3,353,412 issued to Humphrey. The Humphrey apparatus functions to effect sequential triggering of a desired mechanism in accordance with a predetermined schedule. The timing mechanism of the apparatus comprises a drive gear and a gear train which includes a plurality of gear assemblies serially connected in driving relationship with respect to one another and an escapement assembly controls the operation of the gear train.
A typical type of dash pot timer is disclosed in U.S. Pat. No. 3,171,245 issued to Breed. The Breed device comprises a piston that travels in a cylinder at a controlled rate. The movement occurs due to a predictable fluid flow from the forward side of the piston through a predetermined annular clearance between the piston and interior cylinder walls to occupy the ever increasing volume behind the piston.